The present invention relates generally to a system and method that cycles a luminaire, such as one containing a metal-halide lamp, on and off at designated intervals in order to reduce the risk of arc tube rupture. More particularly, the present invention relates to a system and method that repeatedly switches the lamp from a high to low power output state before causing the lamp to extinguish, for a brief period of time, in order to provide a warning to anyone in the general vicinity of the luminaire that the lamp is about to be extinguished.
High intensity discharge (HID) lamps such as metal halide (MH) and high pressure sodium (HPS) lamps have increasingly gained acceptance over incandescent and fluorescent lamps for commercial and industrial applications. HID lamps are more efficient and more cost effective than incandescent and fluorescent lamps for illuminating large open spaces such as construction sites, stadiums, parking lots, warehouses, and so on, as well as for illumination along roadways. An HID lamp comprises an arc-tube containing at least two electrodes, chemical compounds and a fill gas. The fill gas can comprise one or more gases. To initiate operation of the lamp, the fill gas is ionized to facilitate the conduction of electricity between the electrodes. However, these light sources have been found to be susceptible to non-passive lamp failure, or, arc tube rupture.
Non-passive lamp failures generally occur in response to crack propagation of the associated arc tube. Specifically, when the internal arc tube ages and develops minute faults, the arc tube may fracture allowing high pressure to force hot arc tube fragments through the outer glass jacket. If the associated luminaire is not suitably enclosed, falling arc tube fragments may pose a danger to personnel and property. Many luminaires are not enclosed, and accordingly, non-passive end-of-life light source failure is of concern to lamp and luminaire manufacturers.
To prevent the above described situations, high intensity discharge lamp manufacturers recommend periodic cycling of lamps. Where lamps are used in applications that run continuously, lamp manufacturers require regular cycling, typically once a week. In operation, the high wattage light source such as, for example a HID lamp, is periodically cycled off and then back on. As mentioned above, an arc tube that has developed a weakness will most likely fail passively during the cool down and possibly the subsequent warm up cycle. To accomplish the required cycling of these lamps, the lamps should be de-energized and re-energized, per the lamp manufacturer""s recommendations.
Accordingly, an end user could extinguish the lighting from the panel-board on a regular basis, for example, weekly, but there are two flaws in using this method. First, an end user that would operate a facility 24 hours a day/seven days a week would most likely not want to monitor the lighting and whether or not it had been cycled once a week. Secondly, if the end user were to de-energize the luminaire from the panel-board many luminaires would be off at once, probably in the same area, which could become a separate safety issue, in addition to the arc tube failure mentioned above. Although individual timers could be attached to each circuit such an arrangement is a cumbersome solution.
A proposed solution is found in U.S. Pat. No. 6,247,187 to Green, entitled xe2x80x9cSystem for Promoting Passive End of Life Light Source Failure.xe2x80x9d The Green patent discloses a system which automatically energizes and de-energizes a HID light source, however, no warning system is given of the impending power outage. In many applications the lamps are running continuously and an unexpected power outage could be extremely dangerous. For example, suppose a lift truck operator is 15 feet above the ground, for instance in a warehouse environment, and suddenly the luminaire that they are working under goes dark, the operator can experience momentary disorientation or severe enough confusion that could lead to an unfortunate accident.
Accordingly, a need exists for a warning sequence before a luminaire is cycled off to prevent arc tube failure. The high to low cycling of the lamp is much subtler than an abrupt shutdown of the luminaire and would warn people in the area so that they could prepare mentally and physically for the upcoming outage.
It is an object of the present invention to provide a luminaire assembly that comprises a warning sequence before the luminaire de-energizes and energizes in order to reduce the risk of non-passive end of life failure or arc tube rupture.
It is a further object of the present invention to have a self-contained, relatively small circuit that allows the warning function to be retrofit into a conventional metal-halide lamp.
It is yet a further object of the present invention to provide a luminaire assembly that is able to withstand high instantaneous power level changes.
It is still a further object of the present invention to provide a luminaire assembly with a warning feature as well as ae cycling feature for a HID lamp employing either a constant wattage ballast or a magnetically regulated ballast.
These and other objects are substantially achieved by a luminaire assembly comprising a lamp, a ballast, and a microcontroller circuit operable to generate a warning indicator after expiration of a pre-selected period of time. The warning indicator indicates the impending termination of power to the lamp for a pre-determined period of time. Upon expiration of the pre-determined period of time, the microcontroller then restores the power to the lamp and resets the internal timing function.